Advances in molecular biology have allowed the development of biological agents useful in modulating protein or nucleic acid activity or expression, respectively. Many of these advances are based on identifying the primary sequence of the molecule to be modulated. For example, determining the nucleic acid sequence of DNA or RNA allows the development of antisense or ribozyme molecules. Similarly, identifying other primary sequence allows for the identification of sequence that may be useful in creating monoclonal antibodies. However, often the primary sequence of a protein is insufficient to develop therapeutic or diagnostic molecules due to the secondary, tertiary or quarternary structure of the protein from which the primary sequence is obtained. The process of designing potent and specific inhibitors, activators, or novel proteins has improved with the arrival of techniques for determining the three-dimensional structure of an enzyme or polypeptide whose activity one desires to modulate.
The phenylpropanoid synthetic pathway in plants produces a class of compounds know as anthocyanins, which are used for a variety of applications. Anthocyanins are involved in pigmentation and protection against UV photodamage, synthesis of anti-microbial phytoalexins, and are flavonoid inducers of Rhizobium modulation genes 1-4. As medicinal natural products, the phenylpropanoids exhibit cancer chemopreventive activity, as well as anti-mitotic, estrogenic, anti-malarial, anti-oxidant, and antiasthmatic activities. The benefits of consuming red wine, which contains significant amounts of 3,4′,5-trihydroxystilberte (resveratrol) and other phenylpropanoids, highlight the dietary importance of these compounds. One strategy for the generation of novel enzymatic activity in flavonoid biosynthesis uses protein-engineering methods and requires a detailed structural knowledge of enzymes within the targeted pathway.
Polyketides are a large class of compounds and include a broad range of antibiotics, immunosuppressants and anticancer agents which together account for sales of over $5 billion per year. Polyketides are molecules which are an extremely rich source of bioactivities, including antibiotics (e.g., tetracyclines and erythromycin), anti-cancer agents (e.g., daunomycin), immunosuppressants (e.g., FK506 and rapamycin), veterinary products (e.g., monensin), and the like. Many polyketides (produced by polyketide synthases) are valuable as therapeutic agents. Polyketide synthases are multifunctional enzymes that catalyze the biosynthesis of a huge variety of carbon chains differing in length and patterns of functionality and cyclization.
Chalcone synthase (CHS), a polyketide synthase, plays an essential role in the biosynthesis of plant phenylpropanoids. CHS supplies 4,2′,4′,6′-tetrahydroxychalcone (chalcone) to downstream enzymes, such as chalcone isomerase (CHI), that synthesize a diverse set of flavonoid phytoalexins and anthocyanin pigments.
An improvement in the understanding of the structure/function of these enzymes would allow for a number of advances in the art, e.g., the exploitation of the synthetic capabilities of known enzymes for production of useful new chemical compounds, for the creation of novel non-native enzymes having new synthetic capabilities etc. A need exists, therefore, for a detailed understanding of the molecular basis of the chemical reactions involved in polyketide, flavanone and flavonoid synthesis. The present invention addresses this and related needs.